1. Field
The presently disclosed subject matter relates to a light source and a vehicle lamp, and more particularly to a light source device using a plurality of LED chips and to a vehicle lamp such as a headlight, auxiliary headlight, or other vehicle lamp using the light source device.
2. Description of the Related Art
A conventional vehicle lamp that uses a plurality of LED chips for a light source is disclosed in patent document No. 1 (Japanese Patent Application Laid Open JP2005-276805). FIG. 13 of the present application is a schematic cross-section view of a lamp disclosed in patent document 1. The conventional vehicle lamp 1 is a projector-type headlight that includes: an LED light source 2; a first reflector 3a; a second reflector 3b; a third reflector 3c; a projection lens 4; and a shield plate 5.
The first reflector 3a has an elliptic surface that has a first focus F1 located substantially at a central portion of the LED light source 2 so that a major axis thereof corresponds with a light axis in a direction towards the light-emitting direction of the LED light source 2. The elliptic surface has a second focus F2 located substantially at a rearward focus of the projection lens 4. The first reflector 3a reflects light emitted from the LED light source 2 in a direction towards the projection lens 4. The second reflector 3b is an elliptic surface that has a first focus F1 located substantially at the central portion of the LED light source 2 and a second focus F3 located substantially at a position more rearward than the second focus F2 of the first reflector 3a. The third reflector 3c is an elliptic surface that has a first focus located substantially at the second focus F3 of the second reflector 3b and a second focus located substantially at the second focus F2 of the first reflector 3a. The third reflector 3c can alternatively be configured as a parabolic surface that has a central axis corresponding with the above-described light axis.
The projection lens 4 is a convex lens that has a focus located at the second focus F2 of both the first reflector 3a and the third reflector 3c so as to focus the light emitted from the LED light source 2 and/or the light reflected by the first reflector 3a and the third reflector 3c. The shield plate 5 is located substantially at the focus of the projection lens 4 and in the way of the light paths from the LED light source 2 to the projection lens 4 in order to form a cutoff line.
In the vehicle lamp 1 as described above, a part of the light emitted from the LED light source 2 is reflects by the first reflector 3a, focuses at the second focus F2 of the first reflector 3a and emits forward via the projection lens 4. Other parts of the light emitted from the LED light source 2 is reflected by both the second reflector 3b and the third reflector 3c, focuses at the second focus F2 of the third reflector 3c and emits forward via the projection lens 4. Thus, the light emitted from the LED light source 2 forms a light distribution pattern according to the above-described operation and increases light-using efficiency.
FIG. 14 shows a cross-sectional view of an LED light source 2 that is composed, for example, as disclosed in patent document No. 2 (Japanese Patent Application Laid Open JP2004-140090). The conventional LED light source 2 includes: a base 6 that includes a cavity thereon for reflecting light; electrodes 7 are exposed on a bottom surface of the cavity of the base 6; an LED chip 8 is disposed on the bottom surface of the cavity of the base 6, and is electrically connected to the electrodes 7; and, a wavelength conversion material 9.
The cavity in the base 6 is formed as a reflector and expands upward with a slant angle θ that is in the range of 0° to 90°. The LED chip 8 disposed in the cavity of the base 6 is a junction down typed LED, which includes a substrate 8a on a top portion thereof and a light-emitting portion 8b on a bottom portion thereof. Because the substrate 8a is made from a transparent material, light emitted from the light-emitting portion 8b passes through the substrate 8a. The light-emitting portion 8b includes electrodes adjacent thereto that are electrically connected to the electrodes 7. When a power supply introduces electrical current to the light-emitting portion 8b via the electrodes 7, the light emitted from the light-emitting portion 8b emits in a direction towards the substrate 8a directly and by reflecting on the electrodes 7.
The wavelength conversion material 9 is disposed as a layer so as to cover over the cavity of the base 6, and converts the light emitted from the light-emitting portion 8b. For example, a blue light of a blue LED chips is converted into a white light via a yellow/blue color mixture.
At least one side of the LED chip 8 is formed as a straight line to produce a light distribution characteristics of a vehicle lamp. An area of an opening of the cavity in the base 6 is formed smaller than double the area of the light-emitting area of the light-emitting portion 8b in order to increase a luminous flux diverging density of the light emitted upward from the wavelength conversion material 9. The luminous flux diverging density is a luminous flux per unit area that shows 1 m/m2. Therefore, if the luminous flux is the same, the smaller the opening area, the more the luminous flux diverging density increases.
In the above-described LED light source 2, the light emitted from the LED chip 8 emits into the wavelength conversion material 9 both directly and by reflecting on both a side surface of the cavity base 6 and the electrodes 7. The light is then wavelength converted by the wavelength conversion material 9. The wavelength-converted light emits upward with a predetermined light distribution characteristic according to the opening shape of the cavity of the base 6.    1. Patent document No. 1: Japanese Patent Application Laid Open JP2005-276805    2. Patent document No. 2: Japanese Patent Application Laid Open JP2004-140090
In the LED light source 2 according to patent document No. 2, the luminous flux diverging density is high. When a road in front of a vehicle is lighted by an optical structure such as a projection-type headlight and/or a reflection-type headlight, the road located at both a far and a near distance are lighted with a same brightness by the light source with a high luminous flux diverging density. When a driver sees a road lighted by the above-described headlight, the driver recognizes brightness at a nearer portion of the road more than a far portion of it. Thus, because the human eye typically focuses according with the nearer brightness, the visibility for distance decreases.
In addition, when the opening area of the cavity in the base 6 become small, the luminous flux emitted from the opening out of the LED light source 2 decreases. Thus, the LED light source 2 is not favorable for a vehicle lamp due to requiring a high luminous flux.
A conventional light source such as a HID is typically located at a focus of a reflector, in which the focus distance is longer than 20 mm. Because the LED light source 2 is smaller than a HID, it is desirable for a vehicle lamp using the LED light source 2 to be miniaturized by locating the LED light source 2 within the focal distance range of 20 mm. However, such a vehicle lamp has problems such as a short focus distance resulting in a large light distribution pattern. Thus, it is difficult for the LED light source 2 to form a light distribution pattern that is in accordance with light distribution standards.
The disclosed subject matter has been devised to consider the above and other problems and characteristics. Thus, an embodiment of the disclosed subject matter can include LED light sources with a high luminous flux and a favorable brightness distribution, and can include vehicle lamps with a favorable light distribution pattern and which also use LEDs for a light source.